1. Field of the Invention
This invention relates to the field of ultraviolet (UV) flame detectors, infrared (IR) flame detectors, and combination UV/IR flame detectors.
2. Description of the Prior Art
UV/IR detectors for flame detection until this invention utilized photoemissive-cathode electron tubes, such as Geiger-Meuller tubes, in avalanche mode to sense UV radiation from flames.
Concurrent sensing of IR radiation from the flames is performed by UV/IR detectors to confirm presence of flames in the case of hydrocarbon combustion. The utility of existing flame detector devices is limited because of performance factors inherent in the prior art, including the following factors:
The avalanche-mode UV detectors used in flame detectors tend to saturate at moderate levels of input radiation to the extent that they cannot measure accurately the characteristics of radiation from flames in the presence of strong interfering radiation. In order to reduce undesired responses of the avalanche-mode UV detectors to indirect solar radiation, existing flame detectors have utilized photocathodes with spectral sensitivity at wavelengths shorter than 260 nanometers, thus eliminating the capability to sense a major UV spectral emission line associated with hydrogen-oxygen combustion at approximately 305 nanometers wavelength. Predicted future deterioration of the earth's ozone layer, which now prevents short-wave UV solar radiation from interfering with flame detectors, may further reduce the range of flame intensities over which existing detector types are effective in flame detection.
The electronic signal processing capabilities of existing UV/IR type flame detectors are limited. Because avalanche-mode sensor devices produce nearly uniform pulses in response to inputs which may vary widely in intensity, the signal processing elements do not and cannot make use of small variations within the UV radiation intensity profiles of flames and extraneous light sources. Thus, certain significant temporal features of radiation intensity from different sources cannot be used, with products of the prior art, in performance of automatic false-alarm rejection functions.
This invention provides significant improvements in flame detection performance in comparison with existing detection devices which employ IR detectors alone, UV detectors alone, or UV/IR detector combinations with avalanche-mode UV devices. Certain of these improvements in performance arise from greater differences between measurable effects of flames and those of other phenomena i.e., background noise and energy from false alarm sources, that can be achieved by the non-saturating-mode detectors and signal processing circuits of this invention. These greater differences between measurable effects of flames and those of other phenomena achieved by this invention can be exploited to produce increased detection range, detection of smaller flames, reduction of false alarm probability, increased speed of detection response, and combinations of these enhancements. The degree of each of these enhancements is determined in relationship to the others in the embodiments of this invention by selection of appropriate signal processing summation intervals, integration intervals, weighting of sample averages, and threshold parameters.
This invention also provides significant improvements in mechanical and electrical characteristics for use in hazardous environments, when compared to existing flame detector devices that employ high-voltage avalanche-mode detectors. This invention requires only low voltage power supply and only minimal electrical charge storage. Thus the invention provides intrinsic safety in hazardous environments where potentially explosive gases, liquids, or dust are present. These safety characteristics eliminate the need for explosion-proof housings and protection of detector lense/apertures that are common in existing flame detector devices. This invention may thus be manufactured at lower cost and in smaller package size than flame detector devices which require explosion-proof packaging.
Examples of related prior art are found in the following U.S. Pat. Nos. 2,507,359 to P. Weisz; 3,122,638 to D. F. Steele et al; 3,188,593 to A. W. Vasel et al; 3,665,440 to J. M. McMenamin; 3,716,717 to A. Scheidweiler et al; and 4,769,775 to M. Kern et al.